Process for preparing organochlorosilanes

ABSTRACT

Aromatic group containing organochlorosilanes are prepared by irradiating, in the presence of chlorine, a mixture of chlorosilanes of the formula

United States Patent Takamizawa et al.

[ Feb. 15, 1972 PROCESS FOR PREPARING ORGANOCHLOROSILANES inventors: Mlnoru Takamlzawa; Takayoshl Hayashl; Kazumoto Uzawa; Masatoshl Takita; Yoshiaki Kudo, all of Gunma-ken, Japan Assignee: Shinetsu Chemical Company, Tokyo,

.Japan Filed: Sept. 2, 1969 Appl. No.: 854,716

Foreign Application Priority Data Sept. 6, 1968 Japan ..43/64l3l May 1, 1969 Japan ..44/33808 July 26, 1969 Japan ..44/59226 US. Cl. ..204/ 158, 204/ 162 Field of Search ..204/1 58 R, 162

[56] References Cited UNITED STATES PATENTS v 3,188,336 6/1965 Haszeldine ..204/l8l Primary Examiner-Howard S. Williams Attorney-McGlew and Toren [57] ABSTRACT Aromatic group containing organochlorosilanes are prepared by irradiating, in the presence of chlorine, a mixture of chlorosilanes of the fonnula wherein n is 2 or 3 and aromatic compounds. The irradiation is carried out with light, at least 30 percent of the light having a wavelength not exceeding 3,800 A. A wide variety of aromatic group containing organochlorosilanes are selectively obtained by the inventive process with high yields. Further, the formation of byproducts, which are difficult to separate and/or which have no utility, is effectively prevented.

7 Claims, No Drawings FIELD OF THE INVENTION This invention relates to an improved process for preparing,from chlorosilanes containing a SiI-I bond and aromatic compounds,-organochlorosilanes containing aromatic radicals or groups. Organochlorosilanes containing aromatic radicals or groups, such as diphenyldichlorosilane or phenyltrichlorosilanes, are important starting materials for silicone oils, silicon varnishes and silicone rubbers.

PRIOR ART The following four procedures have previously been used for preparing aromatic group containing organochlorosilanes:

a. Grignards method which is practiced by reacting aryltrichlorosilane with halogenated methyl magnesium, or methyltrichlorosilane with halogenated aryl magnesium, for the purpose of obtaining aryl methyldichlorosilane; alternatively, silicon tetrachloride is reacted with halogenated aryl magnesium for the purpose of obtaining aryl trichlorosilane. i b. A method which is practiced by dehydrogenating methyldichlorosilane or trichlorosilane, together with aromatic hydrocarbons, employing boron chloride as a catalyst; or dehydrochlorinating such chlorosilanes by employing chlorinated aromatic hydrocarbons.

. Direct method which is practiced by reacting metallic silicon with chlorobenzene so as to obtain phenylchlorosilanes. I

d. Disproportionation method which is practiced by'reacting phenyltrichlorosilane obtained by Direct method with trimethyl chlorosilane.

All four prior art procedures have, however, serious drawbacks. Grignards method of (a) above has the disadvantage that it requires a large quantity of ether. Further, it is difficult to remove byproducts, a fact which greatly complicates the process. In respect to method (b), the dehydrogenation, and dehydrochlorination have to be conducted at high temperature and/or under high pressures which requires elaborate equipment. Regarding method (0), when the Direct method is adopted, phenyltrichlorosilane, which is the desired product, is obtained merely as a byproduct of diphenyldichlorosilane in small quantity. Particularly when the phenyl group has various substitution radicals, the synthesis by this Direct method often becomes extremely difficult to carry out. Concerning method (d), the Disproportionation reaction method has the disadvantage of having to be practiced under the severe conditions of high temperatures and high pressures, and the reaction product contains unreacted phenyltrichlorosilane which can be separated with great difficulty only.

It has also been suggested as a method for preparing silanes of this kind (cf. specification of U.S.S.R. Pat. No. 162,842) that a mixture of aromatic hydrocarbons and hydrogen chlorosilane, e.g., a mixture of benzene and methyldichlorosilane or of benzene and trichlorosilane, be irradiated with light coming from the source of an incandescent electric lamp, thereby obtaining phenyl methyl dichlorosilane or phenyltrichlorosilane. By this method it is possible to obtain the desired product, unaccompanied by any byproduct which is difficult to separate. However, the yield rate of the desired product, to wit, organochlorosilane containing aromatic radicals or groups, to hydrogen chlorosilane is low. For example,

in the synthesis of phenyl methyl dichlorosilane, the yield rate is l2 percent by weight, and in that of phenyltrichlorosilane, about 39 percent by weight. Even more disadvantageous is in the former case that most of the methyl dichlorosilane turns into worthless methyltrichlorosilane. In the latter case. the unreucted material is converted into worthless silicon telrnchlorlde. Further. it is dilllcult to prepare by this method orgnnochlorosilanes having variable aromatic radicals. The only compounds which can be readily prepared are phenylchlorosilane and phenyl methyl dichlorosilane.

SUMMARY OF THE INVENTION An object of the present invention is to provide a process, free from the above drawbacks, for preparing organochlorosilanes containing aromatic radicals or groups.

Another object of the invention is to provide a process for preparing organochlorosilanes containing variable aromatic radicals, from chlorosilanes having a Si-H bond and aromatic compounds.

A still further object of the invention is to provide a process for preparing such organochlorosilanes at high yield rates, unaccompanied, as much as possible, by byproducts which are hard to separate or of little utility value.

The inventive process is characterized by mixing chlorosilanes containing a Si-H bond and represented bythe general formula I wherein n is an integer of 2 or 3 and an aromatic compound which is represented by the general formula wherein Z is hydrogen, halogen, or a monovalent organic radical selected from the group consisting of alkyl, haloalkyl, alkoxy, phenyl, halophenyl,-phenoxy, phenylmethylene and dialkylamino, and irradiating the mixture, in the presence of chlorine, with light, at least 30 percent of the light having a wavelength not exceeding 3,800 A. By this process, under the conditions of atmospheric pressure and room temperature, organochlorosilanes having variable aromatic radicals can be prepared at good yield rates, accompanied by a minimum amount of byproducts, such as silicon tetrachloride or methyltrichlorosilane, which are of little utility value.

The invention is based on the observation that when the substituted radical, Z, of the aromatic hydrocarbons of the above general formula, is an electron-attractive radical, such as nitro, cyano, carbonyl or trifluoromethyl, the desired reaction will not proceed. By contrast, if said Z is an electrondonative radical, to wit a donor, or a weak electron-attractive radical, such as hydrogen, halogen, alkyl, haloalkyl, alkoxy, halophenyl, phenoxy, phenylmethylene or dialkylamino radicals, the following reaction will rapidly take place, when the mixture is irradiated by the aforementioned light rays:

(cHm-wnSiQZ HC'L The preparation, by this process, of organochlorosilane; containing aromatic radicals, is presumably carried out first by the occurrence of free radicals due to the primary photolysis of chlorine molecules, (C1 2Cl in the reaction system. Said free radicals are supposed to cause hydrogen atoms to isolate themselves from chlorosilanes having Si-H bond, yielding chlorosilyl radicals, which, in turn, react with the benzene nucleus in the aromatic compounds. It was observed in respect to the light source needed for causing the reaction to proceed that, although the chlorine atoms absorbed light covering a wide range of wavelengths with 3,300 A. as the peak, if a large quantity of light with wavelengths of above 5,000 A. was used, the formation of byproducts such as silicon tetrachloride is promoted. Accordingly, in order to prepare only the desired product, viz., organochlorosilanes having aromatic radicals, and at the best yield rate, at least 30 percent, and preferably more than 40 percent. of the radiation light should have a wave length not exceeding 3.800 A. This will be apparent from the fact that when an incandescent light, about 0.5 percent of whose rays have a wavelength not exceeding 3,800 A., is employed,a reaction by which, for example, some phenyltrichlorosilane is prepared,the reaction takes place. However, in such a case, the quantity of light rays whose wavelengths are above 5,000 A. is comparatively large, so that the quantity of silicon tetrachloride formed as byproduct is much increased, as compared with the produc' tion of the desired phenyltrichlorosilane, resulting in turn in a great reduction of phenyltrichlorosilane formation. By the process of the invention, however, phenyltrichlorosilane can be prepared with a yield as high as 70 percent or even more.

A satisfactory light source to be employed in the process of the invention and fulfilling the required conditions may, for example, be a high-pressure mercury lamp, a low-pressure mercury lamp, a xenon arc lamp or a hydrogen arc lamp.

The chlorosilane, which is one of the principal starting materials in practicing the process of the invention, is represented by the general formula:

wherein n is an integer of 2 or 3, and may be exemplified by triehlorosilane and methyldichlorosilane, of which the former is preferred because ofits good reactivity.

The other reactant, to wit the aromatic compound, is represented by the general formula:

wherein Z is hydrogen, halogen or a monovalent organic radical such as alkyl, haloalkyl, alkoxy, phenyl halophenyl, phenoxy, phenylmethylene and dialkylamino radicals. The compounds may be exemplified by benzene or derivatives which have in their benzene nuclei, halogen atoms such as chlorine, fluorine, iodine and bromine, or saturated aliphatic hydrocarbon radicals containing at most 12 carbon atoms, such as methyl, ethyl, propyl, butyl and dodecyl, or haloalkyl radicals such as chloromethyl, B-chloroethyl, y-chloropropyl, y-dichloropropyl, 'y-trichloropropyl, B-fluoroethyl, 'yfl'uoropropyl, y-difluoropropyl and -y-trifluoropropyl, or alkoxy radicals such as methoxy, ethoxy, propoxy and buthoxy, or halophenyl radicals such as chlorophenyl, or dialkylamino radicals such as dimethyl amino, diethyl amino, dipropyl amino and dibutyi amino.

Chiorosilanes having SiH bond and aromatic compounds may be mixed in the mole ratio of from 5:95 to 90:10, or more preferably, from :90 to 70:30. Chlorine, in whose presence the reaction is to be carried out, is supplied, in gaseous phase, to the bottom of the mixture of the above chlorosilanes and aromatic compounds. The amount of chlorine should not be so great so as to cause escape of chlorine in gaseous phase. The radiation reaction may be carried out while the chlorine is being absorbed by the liquid layer. if the chlorine gas has been diluted beforehand with an inert gas such as nitrogen, its absorption by the mixed liquids will take place more uniformly, giving favorable results. The amount of chlorine affects the reaction velocity, so that it may be regulated in accordance with the scale of the reaction, but generally speaking, the quantity of the chlorine supplied throughout the reaction process may be 0.1-3 moles per mole of Si-H radical, or more preferably 0.2-2-moles. As to the reaction time, it may be 5-500 watt per kg of the reaction liquid.

For economy's sake it is preferred that the reaction is carried out at room temperature and atmospheric pressure. However, the success of the reaction is not impaired even if the temperature should rise during operation and while the reaction continuously takes place.

The invention will now be described by several examples, in which the parts are all parts by weight.

EXAMPLE 1 1n the center of a reactor equipped with a reflux cooler, a thermometer and a gas pipe, was installed a 100 watt highpressure mercury lamp. 54 percent of the rays emitted by the light have wave lengths not exceeding 3,800' A. The lamp is so devised as to be cooled on all sides with flowing water. In the reactor were charged 271 parts of trichlorosilane and 1,404 parts of benzene. After the charge was stirred, the atmosphere inside the reactor was replaced by nitrogen gas, and the metcury lamp was lighted. At the same time, chlorine gas was introduced to the bottom of the mixed liquid layer, thereby carrying out the reaction for 3 hours, obtaining 1,71 1 parts of a product consisting of the components given below. The yield rate of phenyltrichlorosilane to the raw material trichlorosilane was 73 percent.

Trichlorosilane 1.9 weight percent Silicon tetrachloride 1.1 weight percent Benzene 60.8 weight percent Phenyltrichlorosilane 15.8 weight percent Substance with high boiling point 20.4 weight percent CONTROL 1 Trichlorosilane 1.9 weight percent Silicon tetrachloride 7.7 weight percent Benzene 65.7 weight percent Phenyltrichlorosilane Substance with high boiling oint 8.4 weight percent 16.5 weight ercent EXAMPLES 2-5 and CONTROLS 2-3 In the center ofa reactor like the one employed in Example 1 was installed a 100-watt high-pressure mercury lamp (54 percent of the rays emitted by which had wave lengths not exceeding 3,800 A.) which was so devised as to be cooled on all sides with flowing water. In the reactor were charged trichlorosilane and various aromatic compounds in the mole ratio of 1:1. While chlorine was being supplied at the rate given in Table l, the reaction was carried out for 5 hours, obtaining the results given in Table 1.

0.5-25 hours, or more preferably, l10 hours. The quantity of As Controls 2 and 3, similar experiments were repeated in light employed in irradiation may be large enough to generate which the only difference was the replacement of the -watt free radicals (Cl in such a quantity as to have the reaction of high-pressure mercury lamp by a 100-watt incandescent electhe invention proceed, viz, 11 ,000 watt or, more preferably tric lamp, obtaining the results also given in Table 1.

TABLE 1 Examples Controls Number 2 3 4 5 2 3 Kind of aromatic compounds Benzene Chlorobenzene.... Toluene DipheHyIethcL... Benzene. Chlorobenzene.

A Quantity 01 trichlorosilane 1,365 542 542 393 1,355 642.

ehnrgt-(i (parts). Quantity 01A charged 780 460 368 493 780 450.

(parts Quantityl 0i)chloriue supplied 64.3 25 23.1 22.5 54.3 25.

(parts/1r. Reaction product to be Phenyltrichlo- Chlorophenyl Tolyltrlehlo- Phenoxyphenyl- Phenyltrlchld Chlorophenylobtained (B). rosilane. trichlorosilane. rosilane. trichlorosilane. rostlanc. trichlorosilane. Quantity of reaction 11 00 940 890 quid 2,197 1 obtained (parts).

TABLE 1 -Conti nugi Examples Controls -Nurnber 2 3 4 5 2 3 Analysis of obtained liquid (percent):

Trichlorosilane 30.2 25.4 37.6 Silicontetraehloride 3.4... 3. UnrcactedA 23.1- 25.4. Quantity oiB prepared... 31.4.. 18.4 Substance with high- 11.9 7.6 0.7

boiling point. Benzyl chloride 5.4 Yield rate of B to tri- 4 60 57 chlorosilane (percent).

CONTROL 4 in Example 9, except that a l00-watt incandescent electric An experiment was conducted, similar to the one in Exampie 5, in which 0.5 percent aqueous solution of potassium bichromate was employed instead of water for cooling the high-pressure mercury lamp. in this manner about 80 percent lamp was used instead of a l00-watt high-pressure mercury lamp, only a tract of phenoxydiphenyl methyl dichlorosilane, which was the desired product, was obtained, and nothing but silicon tetrachloride as a byproduct and unreacted methyldichlorosilane and diphenyl ether, were recovered.

TABLE 2 Examples Control Number 6 7 8 9 6 Kikd of aromatic compounds Benzene Chlorobenzene Toluene ..Diphenylether. Benzene. Quantity ofmethyldichlo- 230 506 675 a 23o.

rosilane charged (parts). Qizanttitg otA charged 156 495 460.....; 597 156.

, par s Quantgyhof chlorine supplied 15 26 25 26 15.

par r. Reaction product to be ob- Phenylmethyl Chlorophenylmethyl Tolylmethyl dichloro- Phenoxyphenyl- Phenylmethyltalned (B). dichlorosilane. dichlorosilane. silane. rplethyldichlorodichlorosilane.

. s ane. Quantity of reaction liquid 402 1, 033 1,085 1,030 408 obtained (parts). Analysis of obtained liquid (percent):

Methyldichlorosilane 28.6 24.7 28.7 21.6 20.3. Methyltrichlorosilane.. 14.2 12.7... 10.5.. 6.9. Unreacted A 27.9 37.2... 29.2. 48.4- Quantity ofB prepared... 23.3...... 20.1... 17.7 16.0 Benzyl chloride 6. 6. Substance with high boil- 6.0 5.3 8.3 7.1 6.6.

ing point. Yield rate of B to methyl- 49.0 42.0 40.7 37.0 12.4.

diehlororosilane.

of the total rays emitted by the lamp had wave lengths of XAMPLE 10 5,4005,800 A. while 19 percent of the light had wave lengths not exceeding 3,800 A. Upon completion of the reaction, the reaction product was refined. The result was that the desired phenoxyphenyl trichlorosilane was obtained as a mere trace and nothing but 250 parts of silicon tetrachloride and 440 parts of diphenyl ether were recovered.

CONTROL 5 Into a reactor similar to the one employed in Example 1 were charged 542 parts of trichlorosilane and 492 parts of nitrobenzene in the mole ratio of 1:1. A 100-watt high-pressure mercury lamp, which was so devised as to be cooled on all sides with flowing water, was lighted, and at the same time chlorine was fed into the reactor at the rate of 23.3 parts per hour. The reaction was conducted while the contents of the reactor were stirred, obtaining the result that nitrobenzene remained unchanged and only trichlorosilane turned into silicon tetrachloride. When benzotrifluoride was employed instead of nitrobenzene in a similar experiment, only trichlorosilane turned into silicon tetrachloride.

EXAMPLES 6-9 and CONTROL 6 Into a reactor used in Example 1 were charged methyldichlorosilane and various aromatic compounds in the mole ratio of 1:1. The light source described in Example 1 was employed. The reaction was carried out as in Examples 2-5, obtaining the results given in Table 2.

Another experiment was conducted as Control 6, in which all the conditions were the same as in Example 6, except that instead of a l00-watt high-pressure mercury lamp, a l00-watt incandescent electric lamp was used. The result is indicated in Table 2. When still another experiment was conducted, just as An experiment was conducted just as in Example 6, except that chlorine was introduced into the bottom of the reactor at the rate of 47 parts per hour, and the reaction was conducted for 5 hours, obtaining 435 parts of product consisting of the components given below. The yield rate of phenylmethyldichlorosilane to methyldichlorosilane was 44.0 percent.

Methyldichlorosilane 7.3 weight percent Methyltrichlorosilanc 23.2 weight percent Benzene 23.5 weight percent 33.3 weight percent l2.7 weight percent Phenylmclhyldichlorosilanc Substance with high boiling point It is to be noted that in the reaction, the quantity of chlorine introduced to the bottom of the mixed liquid layer was large, so that a part of it was not absorbed by the liquid layer but reached the top of the layer and caused vapor phase reaction to take place. turning the contents of the reactor darkish yellow.

EXAMPLE 11 Methyldichlorosilanc 18.3 wcightperccnt after the mixture was stirred, t he atmosphere inside the reacrflhyllrichlvwsilflnc Weight v tor was replaced by nitrogen gas. On lighting the light source, enzcne 25.6 weight percent v PM"y[methyldichlorosilane 293 weight percent chlorine gas was introduced to the bottom of the mixed liquid Suhsmcc high hniling Pain, 93 weigh, percent layer at the rate of 21.6 parts per hour. The reaction was carr ed outfor 5 hours obtaining the results given in Table 3.

TABLE 3 Examples Controls Number. 13 14 15 s 9 1o Light SOlllCO 10 w. low- 100 w. high- 100 w. high- 100 w. high- 100 w. high- 100 w. incandespressure pressure pressure pressure pressure cent electric mercury lamp. mercury lamp. mercury lamp. mercury lamp. mercury lamp. lamp. Cooling method Air-cooled Water-cooled Cooled with Cooled with Cooled with Water-cooled.

aqueous soluaqueous soluaqueous solution of tion of tlon of 0.5% N 1C126H20 1 saturated K2CrzO7. kg./l. CuSO; 0.). Rate of rays having wave- 02 54 36 27 19 0.5.

lengths not exceeding ,800 A. Quantity of reaction liquid 692 690 690 696 703 704.

obtained (parts). Analysis of obtained liquid (percent):

Methyldlchlorosilane 28.7 28.6"" Methyitrichlorosllane 10.5. Benzene 28.4 Phenylmethyldichloro- 25.2

sllane. Substance with high boiling point. Yield rate of phcnylmethyl- 51.1 50.3 45-3 20.3 12.6 11.8.

dichlorosilane to methyldichlorosilane.

EXAMPLE 12 What is claimed is:

in a reactor like the one employed in Example 6 were charged 460 parts of methyldichlorosilane and 312 parts of benzene, and on lighting a 100-watt high-pressure mercury lamp (so devised as to be cooled with flowing water on all sides), chlorine was introduced to the bottom of the mixed liquid layer at the rate of 47 parts per hour. The reaction was conducted for 5 hours, while the reaction temperature was kept at 40-50 C. 833 parts of the product obtained proved to consist of the components given below. The yield rate of phenylmethyldichlorosilane to methyldichlorosilane was 46.4 percent.

11.7 weight percent 18.2 weight percent 26.5 weight percent 33.5 weight percent 10.1 weight percent CONTROL 7 An experiment was conducted similar to the one in Example 12, in which 0.5 percent aqueous solution of potassium bichromate was employed instead of water for cooling the high-pressure mercury lamp. in this manner about 80 percent of the total rays emitted from the lamp has wavelengths of 5,4005,800 A., while 19 percent of the light had wavelengths not exceeding 3,800 A. Upon completion of the reaction, the product obtained proved to consist of the components given below, and the yield rate of phenylmethyldichlorosilane to methyldichlorosilane was as low as l 1.6 percent. The quantity of methyl trichlorosilane byproduced was very large.

Methyldichlorosilanc Methyltrichlorosilane Benzene Phenylmethyldichlorosilane Substance with high boiling point 1.3 weight percent 48.0 weight percent 28.5 weight percent 10.5 weight percent 11.7 weight percent EXAMPLES 13-15 and CONTROLS 8-10 1. A process of preparing aromatic group containing organochlorosilanes, which comprises irradiating, in the presence of chlorine, a mixture of a. chlorosilanes containing a Si-H bond and being represented by the general formula wherein n is an integer of 2 or 3 and b. an aromatic compound of the general formula wherein Z is hydrogen, halogen or a monovalent organic radical selected from the group consisting of alkyl, haloalkyl, alkoxy, phenyl, halophenyl, phenoxy, phenylmethylene and dialkylamino, said irradiation being carried out with light, at least 30 percent of said light having a wavelength not exceeding 3,800 A.

2. The process of claim 1, in which the chlorosilanes and the aromatic compound are mixed in the mole ratio of from 5:95 to :10.

3. The process of claim 1, in which the chlorine introduced into the mixture is diluted with inert as.

4. The process of claim 1, in whic the quantity of chlorine supplied is from 0.1 to 3 mole per mole of Si-H bond in the chlorosilanes.

5. The process of claim 1, in which the amount of light emitted from the light source is from 1 to 1,000 watts per kg. of the reactants in the mixture.

6. A process of preparing aromatic group containing organochlorosilanes, which comprises irradiating, in the presence of chlorine, a mixture of a. methyl hydrogen dichlorosilane and b. an aromatic compound of the formula ganochlorosilanes. which comprises irradiating, in the presence of chlorine. a mixture of a. trichlorosilane and b. an aromatic compound of the formula ##ma t 

2. The process of claim 1, in which the chlorosilanes and the aromatic compound are mixed in the mole ratio of from 5:95 to 90:
 10. 3. The process of claim 1, in which the chlorine introduced into the mixturE is diluted with inert gas.
 4. The process of claim 1, in which the quantity of chlorine supplied is from 0.1 to 3 mole per mole of Si-H bond in the chlorosilanes.
 5. The process of claim 1, in which the amount of light emitted from the light source is from 1 to 1,000 watts per kg. of the reactants in the mixture.
 6. A process of preparing aromatic group containing organochlorosilanes, which comprises irradiating, in the presence of chlorine, a mixture of a. methyl hydrogen dichlorosilane and b. an aromatic compound of the formula wherein Z is hydrogen, halogen or a monovalent organic radical selected from the group consisting of alkyl, haloalkyl, alkoxy, phenyl, halophenyl, phenoxy, phenylmethylene and dialkylamino, said irradiation being carried out with light, at least 40 percent of said light having a wavelength not exceeding 3,800 A.
 7. A process of preparing aromatic group containing organochlorosilanes, which comprises irradiating, in the presence of chlorine, a mixture of a. trichlorosilane and b. an aromatic compound of the formula wherein Z is hydrogen, halogen or a monovalent organic radical selected from the group consisting of alkyl, haloalkyl, alkoxy, phenyl, halophenyl, phenoxy, phenylmethylene and dialkylamino radicals, said irradiation being carried out with light, at least 40 percent of said light having a wave length not exceeding 3,800 A. 